Proteins secreted by the PrsDE type I secretion system in Rhizobium leguminosarum

ZORREGUIETA, A., FINNIE, C., RUSSO, DM Y DOWNIE J.A.

Salt Lake City, Utah, USA

Congreso; American Society for Microbiology (ASM) 102nd General Meeting.; 2002

American Society for Microbiology (ASM)

Proteins secreted by the PrsDE type I secretion system in Rhizobium leguminosarum. Angeles Zorreguieta, Christine Finnnie, Daniela M. Russo and J.Allan Downie The chromosomal prsD and prsE genes of Rhizobium leguminosarum bv. viciae play crucial role in secretion of several proteins. They code for the inner membrane ABC-type transporter (prsD) and the membrane-fusion protein (prsE) components of the type I secretion system. The PrsDE system secretes the signaling protein NodO; two beta 1,4 glycanases, PlyA and PlyB, involved in the EPS processing and other unidentified extracellular proteins. Although the PlyA and PlyB amino acid sequences are very similar, PlyA has extra fifty amino acids at the carboxy-terminus and only PlyB is fully secreted to the extracellular milieu. Although it is known that they are active only when in contact with the specific cell surface through an EPS-related compound, their biological role is still not well understood. To initiate the analysis of regulation of expression and role (s) of PlyA and PlyB we generated operon fusions of plyB and plyA to the lacZ gene using the promoter probe vector pMP220. While both genes reached their highest expression in stationary phase, only plyB expression was increased in the presence of low concentrations of carbon sources and nitrogen, 1mMphosphate and aerobiosis. These results suggest that plyB is induced in the rhizosphere under low nutrient conditions. Expression of plyB was significantly reduced in mutants affected in the regulation or the production of the N-acyl homoserine lactones that mediate quorum sensing. At least seven additional extracellular proteins were absent in the culture medium of the prsD and the prsE secretion mutants. Three of them, EP30, EP32.5 and EP59, showed homology at the amino terminus with Rhizobium extracellular proteins involved in adhesion between bacteria. Confocal microscopy showed that the mutants in the the prsD, prsE and the plyB genes were able to induce aggregates with different architectures compared with the wild type. We propose that the glycanases and the putative adhesions secreted by the PrsDE system regulate the stability and dynamics of the biofilm structure.